The present invention relates to railroad car hot box detectors and more particularly to an improved bearing discriminator circuit for discriminating between readings from roller bearings and friction bearings.
In order to protect against railroad car wheel bearing failure, railroads utilize hot box scanners along their rights of way to scan, through infrared sensitive viewers, the bearings of passing railroad cars. In the event an overheated bearing is detected, the train engineer receives a signal to stop the train and correct the condition before a bearing faiure and possible derailment can occur. Since the unscheduled stopping of a railroad train is a costly and time consuming operation and can totally disrupt schedules it is obviously desirable to enhance as much as possible the accuracy of such hot box detectors.
One problem faced by the designers of hot box detectors is that railroad car wheel bearings are either of the roller bearing or friction bearing (known also as solid and sleeve bearings) variety. While all the bearings on any particular car usually are of the same type, the bearings typically differ from car to car and train to train. Due to physical differences between roller and friction bearings, the output signals from roller bearings are significantly higher (all other factors being equal) than signals from friction bearings. Thus, automatic alarm systems that are based upon amplitude detection must contend with a range of amplitudes that is common to both normal roller bearings and to overheated plain bearings. A discussion of the problems associated with roller-friction bearing discrimination is contained in U.S. Pat. No. 3,812,343 of which I am co-inventor and which is commonly assigned with the present application.
As discussed in the above mentioned patent, it has been observed that there are characteristic differences between the wave shapes and signals generated by passing roller bearings and friction bearings when scanned by a hot box detector such as the SERVOSAFE hot box detective system marketed by the Servo Corporation of America, Hicksville, New York. As shown from FIG. 1, the ideal waveforms of roller and friction bearings may readily be distinguished from one another. Primarily, roller bearing waveforms ideally are generally trapezoidal whereas the friction bearing waveform is sawtooth in shape. Heretofore, discrimination between roller and friction bearings was attained by picking a point in space on every waveform (such as a 1/3 width point) and comparing the amplitude of the waveform at that point with the maximum amplitude. Ideally, for roller bearings the ratio of the maximum value to sample point should be 1:1, while for friction bearings, the ratio should be greater than 1:1. In practice, a ratio of 1.4:1 has been used. While this arrangement has been successfully employed, it can have serious problems when noisy signals are generated. In practice, the roller bearing waveform may often take one of the shapes shown in FIG. 2 with one or more noise generated spikes or notches. The hot box detector system must be able to distinguish between a noisy signal generated from a properly operated roller bearing or an overheat signal generated from a hot friction bearing. That is, if the notch in the roller bearing waveform extends to the sample point the detector could interpret the roller bearing waveform as coming from a friction bearing and since the amplitudes are such to indicate that the friction bearing is overheated, an improper signal to stop the train could be transmitted.
In view of the above, it is the principal object of the present invention to provide an improved discriminator circuit for a hot box detector system.
A further object is to provide such a circuit which can distinguish between signals generated by roller bearings and friction bearings with high probability of success.
A still further object is to provide such a circuit which is relatively simple to produce and may readily be retrofitted into existing equipment.